Fastener, W-containing high-cobalt-nickel secondary hardening steel small-specification bar and preparation method

Abstract

The invention relates to the technical field of ultrahigh-strength and high-toughness steel thermal deformation and thermal treatment production, and particularly discloses a fastener, a W-containing high-cobalt-nickel secondary hardening steel small-specification bar and a preparation method. An intermediate blank bar is heated to a solid solution temperature interval to be subjected to heat preservation solid solution treatment; continuously rolling the intermediate blank bar subjected to solid solution treatment to obtain a small-specification bar primary product; after online sizing blanking is conducted on the small-specification bar primary product, quenching treatment is conducted, and the small-specification bar primary product is cooled to the room temperature; the small-specification bar primary product cooled to the room temperature is subjected to subzero treatment and then is air-cooled to the room temperature, the subzero treatment temperature is smaller than or equal to-73 DEG C, and a subzero bar is obtained; after secondary hardening and tempering treatment is conducted on the deeply-cooled bar, the bar is air-cooled to the room temperature; the diameter of the W-containing high-cobalt-nickel secondary hardening steel small-specification bar ranges from 20 mm to 35 mm. The performance of the material is improved, the production process can be optimized, and the production efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of hot deformation and heat treatment production of ultra-high strength and high toughness steel, and particularly relates to a fastener, a small-sized bar of tungsten-containing high-cobalt nickel secondary hardening steel, and a preparation method thereof. Background Art

[0002] With the development of industrial technology, especially the increasing demand for high-performance fasteners in the fields of aerospace, automotive manufacturing, mechanical equipment, etc. These fasteners need to have excellent strength, toughness and corrosion resistance to adapt to extreme working conditions. High-cobalt nickel secondary hardening ultra-high strength steel has attracted much attention due to its excellent mechanical properties.

[0003] The typical composition and optimal heat treatment system of high-cobalt nickel secondary hardening steel are as follows in the table. Ferrium M54 is a new tungsten-containing secondary hardening ultra-high strength steel designed and developed by QuesTek Innovations LLC. Its strength and toughness are comparable to those of AerMet100 secondary hardening ultra-high strength steel, and its stress corrosion resistance is significantly superior. In addition, its Co content is greatly reduced compared with AerMet100 secondary hardening ultra-high strength steel, resulting in a decrease in production cost, so it has greater application prospects. Ferrium S53 is a new tungsten-containing secondary hardening ultra-high strength stainless steel designed and developed by QuesTek Innovations LLC. China has also successively developed several 1.9 GPa grade ultra-high strength stainless steels, including grades such as S280 and USS122 steel. Among them, high-cobalt nickel secondary hardening steels Ferrium M54, Ferrium S53, S280, USS122G contain 1-1.3% of W. During heat treatment, they require a sufficiently high quenching solution temperature and secondary hardening tempering temperature. The optimal quenching solution temperature for high-cobalt nickel secondary hardening steels Ferrium M54, Ferrium S53, S280, USS122G is ≥1050°C, and the optimal secondary hardening tempering temperature is ≥500°C.

[0004] Table 1: Main alloy element range wt% and optimal heat treatment temperature of typical high-cobalt nickel secondary hardening steel

[0005] A high solution temperature helps alloy elements dissolve more completely into the matrix to form a uniform solid solution, which is beneficial to improving the strength and toughness of the material. When the solution temperature is not high enough, the alloy elements will not dissolve sufficiently, affecting the material strength. However, if the solution temperature is too high, it may also cause grain growth, thereby reducing the strength and toughness of the material.

[0006] The study on the austenite grain growth behavior of high cobalt-nickel secondary hardening steel at different heating temperatures and holding times shows that as the heating temperature increases and the holding time prolongs, the austenite grain size increases. Especially when the heating temperature exceeds 1050 °C, the grain growth rate increases significantly and the grains will undergo severe coarsening. In actual engineering applications, the grain size grade requirement for AerMet100 steel is ≥7, while that for Ferrium M54 steel is ≥4.

[0007] Compared with AerMet100 steel, high cobalt-nickel secondary hardening steels Ferrium M54, Ferrium S53, S280, and USS122G steel containing 1 - 1.3% W with higher secondary hardening tempering temperatures have better thermal softening resistance at 0 - 500 °C. Especially in the temperature range of 400 - 500 °C, compared with AerMet100 steel, they have a significant advantage in thermal softening resistance. Thus, the characteristics of Ferrium M54, Ferrium S53, S280, and USS122G steel to maintain good strength at high temperatures make them ideal materials for manufacturing high-performance fasteners.

[0008] The engineering preparation and application process of W-containing high cobalt-nickel secondary hardening steel bars for fasteners is mainly forging (rolling) bars + normalizing + high-temperature annealing + rough machining + quenching + cryogenic treatment + secondary hardening tempering + finish machining. However, when the existing W-containing high cobalt-nickel secondary hardening steel bars are prepared and applied in fasteners, due to the high quenching solution temperature of ≥1050 °C, the control of grain size has always been a difficult point, and it is often difficult to achieve the best strength-toughness matching target requirements with a grain size of about 6.

[0009] Based on this, the existing technology still needs to be improved. Summary of the Invention

[0010] To solve the above technical problems, embodiments of the present invention propose a fastener, a small-sized bar of W-containing high cobalt-nickel secondary hardening steel, and a preparation method to solve the technical problem that the existing W-containing high cobalt-nickel secondary hardening steel bars cannot meet the application requirements.

[0011] To solve the above technical problems, on the one hand, some embodiments of the present invention disclose a preparation method for a small-sized bar of W-containing high cobalt-nickel secondary hardening steel for fasteners, including: Step 1: Heating the intermediate blank bar to the solution temperature range for holding and solution treatment; Step 2: Continuously rolling the solution-treated intermediate blank bar to obtain a preliminary product of a small-sized bar; Step 3: After online fixed-length cutting of the preliminary product of the small-sized bar, performing quenching treatment and cooling to room temperature; Step 4: After cryogenic treatment of the small-sized bar stock initial product cooled to room temperature within 8 hours, air cool it to room temperature. The temperature of the cryogenic treatment is ≤ -73°C to obtain the cryogenically treated bar stock. Step 5: After subjecting the cryogenically treated bar stock to secondary hardening tempering treatment, air cool it to room temperature. Obtain a small-sized bar of tungsten-containing high-cobalt nickel secondary hardening steel with a diameter of 20 mm - 35 mm. In some embodiments, it further includes: Step 6: After repeating Step 4 and Step 5, obtain a small-sized bar of tungsten-containing high-cobalt nickel secondary hardening steel with a diameter of 20 mm - 35 mm.

[0012] In some embodiments, by mass percentage, in the small-sized bar of tungsten-containing high-cobalt nickel secondary hardening steel, the tungsten content is 1 - 1.3%, Co: 6 - 15%, and Ni: 2 - 12%.

[0013] In some embodiments, in Step 1, the cross-sectional area of the intermediate blank bar stock is more than 20 times the cross-sectional area of the small-sized bar of tungsten-containing high-cobalt nickel secondary hardening steel.

[0014] In some embodiments, in Step 2, the total deformation amount of continuous rolling is more than 95%.

[0015] In some embodiments, in Step 1, the solution temperature range is 1060 - 1085°C, and the holding time for solution heat treatment is 90 - 120 min.

[0016] In some embodiments, in Step 2, the initial rolling temperature of continuous rolling is ≥ 1000°C, the final rolling temperature is ≥ 900°C, and the deformation amount of each rolling pass is balanced.

[0017] In some embodiments, in Step 3, the temperature before quenching treatment is ≥ 700°C; And / or, in Step 3, the water temperature for quenching treatment is controlled below 30°C.

[0018] In some embodiments, the greater the total deformation amount of continuous rolling, the lower the temperature and the shorter the time for secondary hardening tempering treatment.

[0019] On the other hand, the embodiments of the present invention also disclose a small-sized bar of tungsten-containing high-cobalt nickel secondary hardening steel for fasteners, with a grain size of 10.5 - 11.5 grades, a tensile strength of 2189 - 2225 MPa, a yield strength of 1796 - 1836 MPa, an elongation of 13.5 - 14%, a reduction of area of 53 - 55%, and an impact energy of 65 - 70 J; And / or, it is prepared by using the preparation method of the small-sized bar of tungsten-containing high-cobalt nickel secondary hardening steel for fasteners described above.

[0020] In addition, an embodiment of the present invention also discloses a fastener, which is made of the aforementioned small-sized bar of tungsten-containing high-cobalt nickel secondary hardening steel for fasteners.

[0021] Adopting the above technical solution, the present invention has at least the following beneficial effects: A fastener, a small-sized bar of tungsten-containing high-cobalt nickel secondary hardening steel, and a preparation method provided by the present invention simplify the preparation and application processes while improving their strength and toughness. By using a process that tightly combines rolling forming and quenching to prepare a bar with a specification of 20 mm ≤ φ ≤ 35 mm of tungsten-containing high-cobalt nickel secondary hardening steel for fasteners, not only can the material properties be improved, but also the production process can be optimized and the production efficiency can be increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0023] Figure 1 It is a process diagram of a preparation method of a small-sized bar of tungsten-containing high-cobalt nickel secondary hardening steel for fasteners disclosed in some embodiments of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] The following will further describe in detail the embodiments of the present disclosure in conjunction with the drawings. The detailed description and the drawings of the following embodiments are used to exemplarily illustrate the principles of the present disclosure, but cannot be used to limit the scope of the present disclosure. The present disclosure can be implemented in many different forms, not limited to the specific embodiments disclosed herein, but including all technical solutions falling within the scope of the claims.

[0025] These embodiments are provided by the present disclosure to make the present disclosure thorough and complete, and to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that: unless otherwise specifically stated, the relative arrangements of components and steps, the components of materials, numerical expressions and values described in these embodiments should be interpreted as merely exemplary, rather than as limitations.

[0026] It should be noted that in the description of the present disclosure, unless otherwise specified, the meaning of "a plurality of" is greater than or equal to two; the orientation or positional relationship indicated by terms such as "upper", "lower", "left", "right", "inner", "outer", etc. is only for the convenience of describing the present disclosure and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present disclosure. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0027] In addition, the "first", "second" and similar terms used in the present disclosure do not denote any order, quantity or importance, but are only used to distinguish different parts. "Vertical" is not strictly vertical, but within the allowable error range. "Parallel" is not strictly parallel, but within the allowable error range. Terms such as "including" or "comprising" mean that the elements before the term cover the elements listed after the term, and do not exclude the possibility of also covering other elements.

[0028] It should also be noted that in the description of the present disclosure, unless otherwise clearly specified and limited, the terms "installed", "connected" and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected, or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present disclosure can be understood according to specific circumstances. When it is described that a specific device is located between a first device and a second device, there may or may not be an intermediate device between the specific device and the first device or the second device.

[0029] All terms used in the present disclosure have the same meaning as understood by those of ordinary skill in the art to which the present disclosure pertains, unless otherwise specifically defined. It should also be understood that terms defined in a general dictionary, such as, should be interpreted as having a meaning consistent with their meaning in the context of the relevant art, and should not be interpreted in an idealized or overly formal sense, unless specifically defined as such here.

[0030] Technologies, methods and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods and devices should be regarded as part of the specification.

[0031] Such as Figure 1As shown in the figure, some embodiments of the present invention disclose a preparation method for small-sized bars of tungsten-containing high-cobalt-nickel secondary hardening steel for fasteners. Among them, the tungsten-containing high-cobalt-nickel secondary hardening steel mainly refers to a secondary hardening ultra-high strength and high toughness steel with a tungsten content of 1-1.3%, high cobalt, and high nickel. The quenching and solution temperature is ≥1050°C, and typical grades include Ferrium M54, Ferrium S53, S280, and USS122G. The preparation method includes: Step 1: Heat the intermediate billet bar to the solution temperature range for holding and solution treatment. Generally, the cross-sectional area of the prepared intermediate billet bar should be more than 20 times that of the finished bar, and preferably more than 30 times, to ensure that the total rolling deformation is more than 95%, so as to ensure that the bar obtains the best microstructure and properties after rolling. The holding and solution treatment time is generally 90-120 min. The bar can be heated to the optimal solution temperature range of 1060-1085°C and held for 90 min for solution to ensure that alloying elements are fully dissolved while the grains do not grow excessively.

[0032] Step 2: Continuously roll the solution-treated intermediate billet bar to obtain the initial product of the small-sized bar. Generally, the initial rolling temperature is ≥1000°C and the final rolling temperature is ≥900°C, and the deformation of each rolling pass is balanced.

[0033] Step 3: After the initial product of the small-sized bar is cut to a fixed length online, it can be immediately put into a water tank for quenching treatment and cooled to room temperature; generally, after cutting to a fixed length online, the temperature before putting it into the water tank for quenching treatment should be ≥700°C. The water flow in the water tank is circulated, and the water temperature should be controlled below 30°C to ensure sufficient quenching cooling speed.

[0034] Step 4: Perform cryogenic treatment on the initial product of the small-sized bar cooled to room temperature within 8 hours and then air-cool to room temperature. The temperature of the cryogenic treatment is ≤-73°C to obtain the cryogenically treated bar; generally, the holding time of the cryogenic treatment is 80-120 min, preferably 100 min.

[0035] Step 5: After the cryogenically treated bar is subjected to secondary hardening tempering treatment, air-cool to room temperature; generally, the bar can be held in the temperature range of 430-520°C for 6-12 h for secondary hardening tempering treatment and then air-cool to room temperature. For different total deformation amounts, there are different optimal secondary hardening tempering temperatures and times. The greater the total rolling deformation, the lower the secondary hardening tempering temperature and the shorter the time can be.

[0036] Repeat steps four and five when necessary for secondary cryogenic treatment and tempering treatment (which can be judged according to the properties of high-W cobalt-nickel secondary hardening steel grades). Finally, small-sized bars of high-W cobalt-nickel secondary hardening steel with a diameter of 20 mm - 35 mm can be obtained. This repetition is determined based on the requirements for the strength and toughness of the product performance. If a slightly higher strength and toughness are needed, especially when the strength is the same and a higher toughness is required, these two steps can be repeated.

[0037] In this embodiment, the engineering preparation process (heating to above the solution temperature + rolling + bar + normalizing + high-temperature annealing) and application process (rough machining + quenching + cryogenic treatment + secondary hardening tempering + finish machining) of the existing high-W cobalt-nickel secondary hardening steel bars with a specification of 20 mm ≤ φ ≤ 35 mm are combined with the rolling forming and quenching closely to simplify the engineering preparation and application process as: heating to the solution temperature + rolling + online sizing and blanking + cryogenic treatment + secondary hardening tempering + rough machining + finish machining to make fasteners. In this way, the small-sized bars of high-W cobalt-nickel secondary hardening steel for fasteners are prepared to refine the grains and improve their application strength and toughness at the same time.

[0038] For the conventional engineering preparation and application process of high-W cobalt-nickel secondary hardening steel, because quenching + cryogenic treatment + secondary hardening tempering treatment are required after rough machining during application, its high quenching solution temperature of ≥ 1050 °C results in the grain size generally being controlled at about grade 6, and it is difficult to achieve the best matching goal of strength and toughness.

[0039] Combining the rolling forming of the bar and the application quenching closely simplifies the engineering preparation and application process as: heating to the solution temperature + rolling + quenching + cryogenic treatment + secondary hardening tempering + rough machining + finish machining. The advantages of the small-sized bar preparation and application to fasteners in this technical solution are as follows: During the process of heating to the solution temperature + rolling + quenching + cryogenic treatment + secondary hardening tempering, it will cause the formation of an ultrafine-grained martensite structure in the steel, which has a high density of dislocations, nano-scale M2C precipitation hardening, and nano-scale reverse transformation austenite films. This structure provides excellent strength and toughness, enabling the steel to have good ductility while maintaining high strength.

[0040] Rolling accelerates the precipitation process of M2C carbides by increasing the dislocation density and providing more precipitation phase nucleation sites, changing the kinetics of M2C precipitation and reverse transformation austenite precipitation, which allows the use of a lower tempering temperature or a shorter tempering time. After tempering secondary hardening, although the dislocation density decreases, the precipitation hardening compensates for the strength loss due to dislocation recovery, and the precipitation of reverse transformation austenite further increases the toughness.

[0041] After rough machining, there is no need for quenching + cryogenic treatment + secondary hardening tempering treatment. It does not need to go through a high quenching solution temperature of ≥1050°C, and there is no need to worry about the grain growth tendency during high-temperature solution. The grain size can be controlled at grade 10 or above, which results in higher strength and better toughness.

[0042] The present invention will be described in detail below in conjunction with specific embodiments, but the present invention is not limited thereto.

[0043] A preparation method for a W-containing high-cobalt nickel secondary hardening steel bar with a specification of 20mm ≤ φ ≤ 35mm uses a process that combines rolling deformation and quenching heat treatment to engineer the preparation and application of small-sized W-containing high-cobalt nickel secondary hardening steel bars, simplifies the process while refining the grains and improving their strength and toughness. The specific steps of its preparation method: intermediate billet preparation + solution treatment + continuous rolling + quenching treatment + cryogenic treatment + secondary hardening tempering treatment. The following examples mainly describe the examples in conjunction with Ferrium M54 steel.

[0044] Example 1: For Ferrium M54 steel, prepare a 150mm * 150mm square billet, heat it in a heating furnace to 1060°C and hold for 90 minutes, continuously roll it to a φ20mm specification, cut it to a fixed length online, quench it in a water tank to room temperature, immediately (within 2 hours) perform a cryogenic treatment at -73°C for 100 minutes and then air cool back to room temperature, and perform a secondary hardening tempering treatment at 490°C * 10h. Carry out rough machining and finish machining applications.

[0045] Example 2: For Ferrium M54 steel, prepare a 150mm * 150mm square billet, heat it in a heating furnace to 1060°C and hold for 90 minutes, continuously roll it to a φ25mm specification, cut it to a fixed length online, quench it in a water tank to room temperature, immediately (within 8 hours) perform a cryogenic treatment at -73°C for 100 minutes and then air cool back to room temperature, and perform a secondary hardening tempering treatment at 490°C * 10h. Carry out rough machining and finish machining applications.

[0046] Example 3: For Ferrium M54 steel, prepare a 150mm * 150mm square billet, heat it in a heating furnace to 1060°C and hold for 90 minutes, continuously roll it to a φ30mm specification, cut it to a fixed length online, quench it in a water tank to room temperature, immediately (within 8 hours) perform a cryogenic treatment at -73°C for 100 minutes and then air cool back to room temperature, and perform a secondary hardening tempering treatment at 500°C * 10h. Carry out rough machining and finish machining applications.

[0047] Example 4: Ferrium M54 steel, prepare a 150mm * 150mm square billet, heat it in a heating furnace to 1060 °C and hold for 90 min, continuously roll it to a φ35mm specification, cut it to a fixed length online, quench it in a water tank to room temperature, and immediately (within 2 hours) perform cryogenic treatment at -73 °C for 100 min and then air return to room temperature, and perform secondary hardening tempering treatment at 500 °C for 10 h. For rough machining and finish machining applications.

[0048] Comparative Example 1: Ferrium M54 steel, prepare a 150mm * 150mm square billet, heat it in a heating furnace to 1060 °C and hold for 90 min, continuously roll it to a φ35mm specification, cut it to a fixed length online, quench it in a water tank to room temperature, and perform cryogenic treatment at -73 °C for 100 min and then air return to room temperature after 24 h, and perform secondary hardening tempering treatment at 500 °C for 10 h. Detect the performance.

[0049] Table 2 Grain size, strength and toughness of Ferrium M54 steel bars in examples and comparative examples during application

[0050] As can be seen from Table 2, in Examples 1-4, the grain sizes of Ferrium M54 steel bars with φ20, φ25, φ30, and φ35mm specifications for fasteners are 11.5, 11, 10.5, and 10.5 grades respectively, and the corresponding tensile strengths are 2189 - 2225 MPa, yield strengths are 1796 - 1836 MPa, elongation rates are 13.5 - 14%, reduction of area rates are 53 - 55%, and impact energies are 65 - 70 J. By using the preparation scheme for small-sized bars that tightly combines rolling forming and quenching, the grain size of Ferrium M54 steel can be increased from 6 - 7.5 grades to 10 grades and above, while the tensile strength reaches 2200 MPa and the impact energy is above 65 J. For the Ferrium M54 steel bar with a φ20mm specification in Comparative Example 1, the corresponding grain size is 11.55 grades. Because it was not cryogenically treated at -73 °C in time within 8 hours after water quenching, its corresponding tensile strength is 2075 MPa, yield strength is 1665 MPa, elongation rate is 14%, reduction of area rate is 55%, and impact energy is 60 J. The strength and toughness matching is lower than that of Examples 1-4.

[0051] Adopting the technical scheme of tightly combining rolling forming and quenching described in the present invention is particularly suitable for producing small-sized bars for fasteners made of high-cobalt nickel secondary hardening ultra-high strength steel with a high solid solution temperature of W.

[0052] So far, the embodiments of the present disclosure have been described in detail. To avoid obscuring the concept of the present disclosure, some details well known in the art have not been described. Those skilled in the art can fully understand how to implement the technical solutions disclosed herein based on the above description.

[0053] Although some specific embodiments of the present disclosure have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the present disclosure. Those skilled in the art should understand that the above embodiments can be modified or partial technical features can be equivalently replaced without departing from the scope and spirit of the present disclosure. In particular, as long as there is no structural conflict, the various technical features mentioned in each embodiment can be combined in any way.

Claims

1. A method for preparing small-sized bars of W-containing high-cobalt-nickel secondary hardened steel for fasteners, characterized in that: include: Step 1: heating the intermediate billet bar to the solution temperature range for heat preservation and solution treatment; Step 2: continuously rolling the intermediate billet bar after solid solution to obtain a small-sized bar product; Step 3: After the small-size bar is cut into pieces online, it is quenched and cooled to room temperature; Step 4: After the small-sized bar product is cooled to room temperature within 8 hours, it is subjected to deep-cryogenic treatment, and then air-cooled to room temperature, wherein the temperature of the deep-cryogenic treatment is ≤-73°C, to obtain a deep-cooled bar; Step 5: After the deep cooling, the bar is subjected to secondary hardening and tempering treatment, and then air-cooled to room temperature; The obtained small-size bars are high-cobalt-nickel secondary hardening steel bars with a diameter of 20 mm to 35 mm.

2. The method for preparing small-sized bars of W-containing high-cobalt-nickel secondary hardening steel for fasteners according to claim 1, characterized in that: Also includes: Step 6: After repeating steps 4 and 5, a small-sized bar of W-containing high-cobalt-nickel secondary hardening steel with a diameter of 20 mm to 35 mm is obtained.

3. The method for preparing small-sized bars of W-containing high-cobalt-nickel secondary hardening steel for fasteners according to claim 1, characterized in that: In terms of mass percentage, in small-sized bars of W-containing high-cobalt-nickel secondary hardening steel, the W content is 1-1.3%, Co: 6-15%, and Ni: 2-12%.

4. The method for preparing small-sized bars of W-containing high-cobalt-nickel secondary hardening steel for fasteners according to claim 1, characterized in that: In step 1, the cross-sectional area of ​​the intermediate billet bar is more than 20 times the cross-sectional area of ​​the small-sized bar of W-containing high-cobalt-nickel secondary hardened steel.

5. The method for preparing small-sized bars of W-containing high-cobalt-nickel secondary hardening steel for fasteners according to claim 1, characterized in that: In step 2, the total deformation of continuous rolling is more than 95%.

6. The method for preparing small-sized bars of W-containing high-cobalt-nickel secondary hardening steel for fasteners according to claim 1, characterized in that: In step 1, the solution temperature range is 1060-1085°C, and the time of the solution treatment is 90-120 minutes.

7. The method for preparing small-sized bars of W-containing high-cobalt-nickel secondary hardening steel for fasteners according to claim 1, characterized in that: In step 2, the initial rolling temperature of the continuous rolling is ≥1000°C, the final rolling temperature is ≥900°C, and the deformation of each rolling pass is balanced; And / or, in step 3, the temperature before quenching treatment is ≥ 700°C; And / or, in step three, the water temperature of the quenching treatment is controlled below 30°C.

8. The method for preparing small-sized bars of W-containing high-cobalt-nickel secondary hardening steel for fasteners according to claim 1, characterized in that: The greater the total deformation of continuous rolling, the lower the temperature and the shorter the time of secondary hardening and tempering treatment.

9. A small-sized bar of high-cobalt-nickel secondary hardened steel containing W for fasteners, characterized in that: The grain size is 10.5-11.5, the tensile strength is 2189-2225 MPa, the yield strength is 1796-1836 MPa, the elongation is 13.5-14%, the cross-sectional reduction is 53-55%, and the impact energy is 65-70 J; And / or, it is produced by the method for preparing small-sized bars of high-cobalt-nickel secondary hardening steel containing W for fasteners as described in any one of claims 1 to 8.

10. A fastener, characterized in that: The fastener described in claim 9 is made of small-sized bars of W-containing high-cobalt-nickel secondary hardened steel.

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